Journal of
Threatened Taxa | www.threatenedtaxa.org | 26 October 2018 | 10(11):
12531–12537
Habitat distribution modeling for reintroduction and conservation of Aristolochia indica L. - a threatened
medicinal plant in Assam, India
Bhaskar Sarma 1,
Prantik Sharma Baruah
2 & Bhaben Tanti
3
1 Department of Botany, Anundoram
Borooah Academy Degree College, Pathsala,
District- Barpeta, Assam 781325, India
2,3 Department of Botany, Gauhati
University, Guwahati, Assam 781014, India
1 bhaskarsarma252@gmail.com, 2 prantik16@yahoo.com,
3 btanti@gauhati.ac.in (corresponding author)
Abstract: A detailed study on the regeneration
ecology of Aristolochia indica
L. was carried out to prevent this threatened medicinal plant from its future
extirpation in Assam, India. The population stock of the species has been
depleting fast in its natural habitats as a consequence of certain factors such
as habitat fragmentation, over-exploitation due to its high medicinal
properties, and other anthropogenic activities. For improving the conservation
status of the species, potential area and habitat for its reintroduction were
predicted using Maximum Entropy distribution modelling algorithm. The model was
developed using environmental parameters and locality data in the natural range
of Karbi Anglong District
of Assam, India. The model predicted that the suitable habitats for the
reintroduction of A. indica L. were restricted
to parts of Assam, Nagaland, Meghalaya, and Arunachal Pradesh
which have been identified to offer suitable environmental conditions
for persistence of the species. Population status was positively correlated
with higher model thresholds in the undisturbed habitats confirming the
usefulness of the habitat model in population monitoring, particularly in
predicting the successful establishment of the species.
Keywords: Aristolochia indica, Assam, conservation, habitat
distribution modelling, India, MaxEnt, NDVI,
reintroduction, threatened.
doi: http://doi.org/10.11609/jott.3600.10.11.12531-12537
Editor: K. Haridasan, Palakkad, Kerala, India. Date
of publication: 26 October 2018 (online & print)
Manuscript details: Ms # 3600 |
Received 24 June 2017 | Final received 12 September 2018 | Finally accepted 08
October 2018
Citation: Sarma, B., P.S. Baruah
& B. Tanti (2018). Habitat distribution modeling for reintroduction and conservation of Aristolochia indica
L. - a threatened medicinal plant in Assam, India. Journal of Threatened
Taxa 10(11): 12531–12537; http://doi.org/10.11609/jott.3600.10.11.12531-12537
Copyright: © Sarma et al. 2018. Creative Commons Attribution 4.0
International License. JoTT allows
unrestricted use of this article in any medium, reproduction and distribution
by providing adequate credit to the authors and the source of publication.
Funding: None.
Competing interests: The authors declare no competing interests.
Author Details: Bhaskar Sarma, Assistant Professor, Department of Botany, Anundoram Borooah Academy
Degree College, whose interest in cytogenetics, plant
breeding, molecular biology and ecological modeling. Prantik Sharma Baruah, research scholar,
Department of Botany, Gauhati University. His research interest in cytogenetics,
plant tissue culture and ecological modeling. Bhaben Tanti,
Professor, Department of Botany, Gauhati University.
His research interest in cytogenetics, plant
breeding, molecular biology and stress physiology.
Author Contribution: BS carried out the survey and execution of experiments. PSB prepared the
manuscript. BT conceived and designed the experiment and critically analyzed
the data. All authors read and approved the final manuscript.
INTRODUCTION
Rapidly
changing climate, habitat fragmentation & loss, invasion of alien species
& pathogens, over-exploitation, and rapid urbanization are the most
important factors responsible for ecosystem degradation worldwide that alter
the structural and functional integrity of ecosystems (Barnosky
et al. 2011; Baruah et al. 2016). In addition to
these, rising temperatures and rapid economic development, and can potentially
affect ecosystems, rapidly disassemble communities, and negatively impact
native biodiversity (Sanders et al. 2003; Lin et al. 2007; Thuiller
et al. 2007; Kelly & Goulden 2008; Walther 2009).
Such alterations have brought approximately one-fifth of plant species to the
brink of extinction (Brummitt & Bachman 2010).
Species (re)introduction is one of the successful
ecological engineering techniques for the restoration of depleted species
populations and degraded habitats &ecosystems (Leaper et al. 1999;
Martinez-Meyer et al. 2006; Kuzovkina & Volk
2009; Ren et al. 2009; Rodríguez-Salinas et al. 2010;
Polak & Saltz 2011). In
order to reintroduce and rehabilitate the threatened species in terrestrial
ecosystems, a detailed knowledge on the distribution of their potential
habitats is essential. Habitat distribution modeling,
therefore, helps to identify the areas for species reserves &
reintroduction, and in developing effective species conservation measures.
Habitat distribution modeling is a computer-based tool which uses algorithms to relate known occurrences of a
species across landscapes to digital raster geographic information system (GIS)
coverage summarizing environmental variation across the landscapes to develop a
quantitative picture of the ecological distribution of the species. New
insights into the factors governing the distribution of species have been
developed using habitat distribution modeling or
ecological niche modeling (ENM) (Guisan
& Zimmermann 2000; Elith et al. 2006; Kozak et al. 2008). The technique of ENM uses computer
algorithms that predict species distribution in a geographic space based on the
mathematical representation of the ecological niche of the species. ENM
considers environmental factors such as temperature,
precipitation, soil, vegetation & land cover as ecological conditions and
uses the dataset from GIS databases such as www.worldclim.org
&www.diva-gis.org. Availability of high-resolution satellite imageries,
downscaling tools for environmental variables, and interpolated spatial
datasets on climate and vegetation has enhanced the accuracy of prediction of
the models manifold. ENM facilitates interpolation as well as extrapolation of
species distributions in geographic space across different time periods. This
has made it possible to prepare species distribution maps with a high level of
statistical confidence and to identify areas suitable for reintroduction of
threatened species (Irfan-Ullah et al. 2006;
Martinez-Meyer et al. 2006; Kumar & Stohlgren
2009; Ray et al. 2011; Sarma et al. 2015; Sarma & Tanti 2017).
Identification
of suitable habitats for the reintroduction of species is the next logical step
in species conservation effort. Therefore, the present work was undertaken to
model the potential habitat distribution of Aristolochia
indica L., a threatened medicinal plant species
in northeastern India, in its native range.
MATERIALS AND METHODS
Plant
materials
Aristolochia indica L. is a climber which
belongs to the family Aristolochiaceae. The plant is
a shrubby or herbaceous vine with a woody rootstock (Kanjilal
et al. 2009). The leaves are glabrous, variable,
usually obovate-oblong to sub-pendurate
entire with undulate at the margins, cordate
acuminate at the base. Flowers few, in axillary racemes with a perianth upto 4 cm long having a glabrum pale green inflated (Das et al. 2010). It is mostly distributed along
tropical, subtropical, and Mediterranean regions of the world(Sarma & Tanti 2015; Neinhuis
et al.2005; Wanke et al. 2007).The plant is used to
treat cholera, intermittent fever, bowel troubles, ulcers, leprosy, and
poisonous bites (Krishnarajuet al.2005; Kanjilalet al.2009). It is also used for its emmenagogue, abortifacient,
antineoplastic, antiseptic, anti-inflammatory, and antibacterial properties (Achari et al. 1981; Das et al. 2010).
Habitat distribution modeling
Sixteen
primary distributional records of the species were collected through field
surveys. The coordinates of all the occurrence points were recorded to an
accuracy of 10–40 m using a Global Positioning System (GarminEdge-1000). The
coordinates were then converted to decimal degrees for use in modeling the distribution of potential habitats of the
species in its native range. Over the years, a variety of environmental
datasets have accumulated in public domain websites, which can be used in
distributional modeling of species. Use of different
formulation of environmental datasets, however, yields different results for
the same set of species (Peterson & Nakazawa
2008). Hence, selection of appropriate data type and pixel resolution is a
prerequisite prior to predictive modeling (Parra et al.
2004). In the present study, normalized difference vegetation index (NDVI) was
used to summarize the habitat boundaries for the species in northeastern
India. All the analyses were conducted at the spatial resolution of 250m.
Validation of model robustness
Following
standard methods, the potential habitat of A. indica
L. was defined as ‘a habitat which bears a set of ecological conditions that
allows the species to persist and regenerate.’ For habitat modeling,
the pixel dimension was a 250 × 250 m grid cell and the model was developed
using maximum entropy modeling (Max-Entversion 3.3.3e, Phillips et al. 2006). MaxEnt estimates the maximum entropy probability
distribution function to predict the geographic location of a species based on
environmental variables and reconstructs the boundaries of the ecological niche
by placing constraints on the probability distribution based on the
environmental parameters of the grid-cell presence record (Phillips et al.
2006). It is one of the ‘presence-only’ group of
species distribution modeling methods that has been
widely used. The strong attributes of MaxEnt are:
It
holds a strict mathematical definition.
It
gives a continuous probabilistic output.
It
simultaneously handles both continuous and categorical environmental data.
It
investigates variable importance through jackknife
procedure.
It has
the capacity to handle low sample sizes.
Its simplicity for model interpretation (Elith
et al. 2006; Phillips et al. 2006; Pearson et al. 2007).
It also facilitates replicated runs to allow
cross-validation, bootstrapping, and repeated sub-sampling in order to test
model robustness.
Of the
16 records, 75% were used for model training and 25% for testing. To validate
the model robustness, we executed 20 replicated model runs for the species with
a threshold rule of 10 percentile training presence. In the replicated runs, we
employed a cross-validation technique where samples were divided into replicate
folds and each fold was used for test data. Other parameters were set to
default as the program is already calibrated on a wide range of species
datasets (Phillips & Dudík 2008). From the
replicated runs, average, maximum, minimum, median, and standard deviation were
generated. Model quality was evaluated based on area under curve (AUC) value
and the model was graded following Thuiller et al.
(2005) as poor (AUC < 0.8), fair (0.8 < AUC < 0.9), good (0.9 < AUC
< 0.95), and very good (0.95 < AUC < 1.0). Further, potential area of distribution and/or reintroduction were categorized
into five classes based on logistic threshold of 10 percentile training
presence, i.e., very-high (0.762–1), high (0.572–0.761), medium (0.381–0.571),
low (0.325–0.570), and very low (0–0.324).
Population status vis-à-vis model
thresholds
Extensive
field surveys were carried out in order to explore the robustness and
pertinence of the model in predicting the population status of the species in
each occurrence locality as predicted under various model thresholds. The total
population of the species was ascertained through a direct count of all the
individuals of seedlings, saplings, and mature individuals in each 250×250 m
grid of occurrence within the predicted localities. The population data of A.
indica L. in each locality was then correlated
with the corresponding threshold level of the distribution models to assess
whether regions covered in the higher thresholds maintain higher populations
thus approving better habitat conditions for species establishment and vice
versa.
Assessment of habitat status and
identification of areas for reintroduction
Assessment
of the actual habitat type of the species in the localities of occurrence as
well as in the entire predicted potential area was done through repeated field
surveys. We also superimposed the predicted potential areas on Google Earth
Ver. 6 (Deka et al., 2018) imageries for habitat
quality assessment. The predicted suitability maps were exported in KMZ format
using Diva GIS ver. 7.3 (Baruah et al. 2016). KMZs are zipped Keyhole Markup
Language (KML) files that specify a set of features such as place marks,
images, polygons, 3D models, or textual descriptions for display in Google
Earth. The exported KMZ files were overlaid on satellite imageries in Google
Earth to ascertain the actual habitat condition prevailing in the areas of
occurrence (Adhikari et al. 2012; Deka
et al. 2017).
RESULTS
Calibration of models
The model calibration test for A. indica
L. yielded satisfactory results (AUCtest = 0.95 ±
0.002). The highest
percent contribution was given by eu7_1_eur (July),
i.e., 29.3%. eu7_1_eurhad the maximum influence on the
habitat model. Jackknife analysis revealed that the
environmental variable with the highest gain, when used in isolation, is eu7_1_eur,
which therefore appears to have the most useful information by itself. The
environmental variable that decreases the gain the most when it is omitted is
eu2_1_eur(February), which therefore appears to have
the most information that is not present in other variables. Bioclimatic
variables did not show any major contribution to the development of the model.
Potential habitat distribution area for
reintroduction
In our
field survey, we found the species only in some parts of Karbi
Anglong District of Assam, India. When we
superimposed the data with Google Earth, the suitable habitats where the
species can be conserved and reintroduced were distributed in various parts of
Assam, Nagaland, Meghalaya, and Arunachal Pradesh. Besides, some areas of
Bhutan were also suitable for the reintroduction (Image 1).
Analysis of variable contributions
Table 1
gives estimates of relative contributions of environmental variables to the MaxEnt model. To determine the first estimate, in each iteration of the training algorithm, the increase in
regularized gain is added to the contribution of the corresponding variable, or
subtracted from it if the change to the absolute value of _ is negative. For
the second estimate, for each environmental variable, in turn, the values of
that variable on training presence and background data are randomly permuted.
The model is re-evaluated on the permuted data and the resulting drop in
training AUC is shown in the table, normalized to percentages. As with the
variable jackknife, variable contributions should be
interpreted with caution when the predictor variables are correlated. Values
shown are averages over replicate runs (Table 1).
Figure
1 shows the results of the jackknife test of variable
importance. The environmental variable with the highest gain, when used in
isolation, is eu7_1_eur, which therefore appears to have the most useful
information by itself. The environmental variable that decreases the gain the
most when it is omitted is eu2_1_eur, which therefore appears to have the most
information that isn’t present in the other variables. Values shown are
averages over replicate runs (Baruah et al. 2018; Das
et al. 2018).
Table 1. List of NDVI and variable
contribution used in the model
Variable |
Percent contribution |
Permutation importance |
eu8_1_eur |
25.7 |
0 |
eu7_1_eur |
29.3 |
64.2 |
eu2_1_eur |
20 |
5.7 |
eu10_1_eur |
12.5 |
17.3 |
eu3_1_eur |
6.1 |
1.7 |
eu11_1_eur |
4.5 |
9.2 |
eu5_1_eur |
1.4 |
1.2 |
eu4_1_eur |
0.3 |
0.3 |
eu6_1_eur |
0.2 |
0.3 |
eu12_1_eur |
0.1 |
0.1 |
eu1_1_eur |
0 |
0 |
eu9_1_eur |
0 |
0 |
DISCUSSION
Model
output and field surveys revealed that suitable natural habitats of the species
concurred with the distribution of humid subtropical forests. NDVI parameters
offered a reasonable explanation on the underlying role of other environmental
factors that determined the habitat suitability of the species. Various
environmental factors such as geology, soil, and climate have a plausible
influence on vegetation indices of a given place at a given time (Soleimani et al. 2008). The effects of such underlying environmental
factors are reflected throughthe spatial and temporal
variation in vegetation indices such as NDVI. Hence, NDVI also act as powerful
and informative surrogate variables, representing the complex formulations of
the underlying environmental factors that determine the boundaries of the
potential habitat of species. Overall, the results of actual habitat assessment
through Google Earth superimposition and field surveys were identical. Habitat
status assessment through primary field surveys and secondary surveys using
Google Earth satellite imageries revealed that the predicted potential areas of
the species under all suitability threshold levels, i.e., low to very high
suitability, encompass a mosaic of disturbed/undisturbed forest patches, scrubs,
grasslands, and human-generated land use elements such
as rural/urban settlements, settled cultivation areas, homestead gardens, and
small groves, which essentially are components of the anthropobiome
(Tanti et al. 2010). Species reintroduction plans should therefore carefully
select appropriate areas under such a setting. In the present study, some areas
consisting of continuous and intact patches of subtropical broadleaved and
degraded forest patches offer potential habitats at higher levels of probability.
Hence, such forest areas could serve as habitats for in situ conservation and
reintroduction. Predicted less suitable areas such as small groves and
homestead gardens, however, could also be used for reintroduction of the
species provided that adequate measures are taken for habitat protection. To
achieve this, awareness and active participation of local people,
non-government organizations (NGOs), and community based
organizations are warranted. The present study demonstrates that habitat
distribution modeling could be of great help in
predicting the potential habitats of threatened species for reintroduction.
Results of the study also suggest the strong relationship between the
population size and model thresholds, thereby indicating the high potential value
of ENM in population studies. The areas identified in the present study for the
reintroduction of A. indica would not only
help in ecorestoration of degraded forests and
habitats where the species had existed before but also in rehabilitating the
species population and improving its conservation status. Therefore, the
results would be quite useful for natural resource managers in the management
of this species and conservation of overall biological diversity in the region.
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